In the cement industry it is customary practice to use a so-called cyclone preheater for preheating the cement raw meal prior to its being burned in a kiln into cement clinker which is subsequently cooled in a clinker cooler. Typically, a cyclone preheater comprising four to six cyclone stages is used arranged in a preheater tower construction. The raw meal is introduced in the first cyclone stage and heated by direct contact with hot exhaust gases from the kiln according to the counter flow principle. Preheaters of this kind are generally known from the patent literature and one example is provided in EP 0 455 301.
A well-known limitation of the capacity of such pre-heater towers is the building costs of such towers easily exceeding 100 meters nowadays. Consequently civil construction costs are very high for these preheater towers. One aspect especially makes the construction costs very high for these towers namely that they are dimensioned after the weight of the all cyclones including the material present in the cyclones. During operation the weight of material in the separator cyclone stages are not very high, since the raw meal is suspended in an air stream. However, if the outlet of the cyclones for some reason clog up the cyclones will gradually fill up the entire inner space of the cyclones until the inlet of the cyclone is also clogged. A cyclone stage completely filled with compacted raw mill adds several tons to the empty weight of the cyclone and thereby to the preheater tower construction. When dimensioning a preheater tower, the construction must typically be dimensioned according to worst case scenarios. Typically the maximum filling level of the cyclones is a critical parameter. All preheater towers are dimensioned to accommodate even critical situations when filling levels become close to the worst case scenario e.g. due to clogging.
Therefore it would be advantageous to be able to construct a preheater tower and preheater system with the ability to minimize the worst case scenario weight of the cyclones filled to their maximum filling level such that capacity may be increased without burdening the construction costs severely in these tall constructions.
Another aspect also that makes it necessary to build these very high towers is the need for high production rates with high temperature differences. Maintaining high production rates at high temperature differences require optimal heat exchange between air and raw meal material.
Therefore it would also be advantageous to be able to construct a preheater tower and preheater system with the ability to improve heat exchange compared to the prior art to decrease height of these towers or maximize production rates at the same height or even allow for less preheater stages to be used by using less separators in the towers.